EXPLANATION OF THE ILLUSTRATION 
Puare XXVII. Tripsacoid (A,C) and non-Tripsacoid 
(B,D) cobs from Richards’ Caves which have been 
subjected to ten hours (A,B) and twenty-four hours 
(C, D) of erosion by sulphuric acid. The treated 
portions are uppermost in the illustration. Note 
that in both treatments the Tripsacoid or lignified 
cobs are more resistant to the action of the acid. 
For example, the non-Tripsacoid cob (D) has dis- 
integrated to a delicate framework of cupule mar- 
gins. Natural size. 
